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Yu Wang - One of the best experts on this subject based on the ideXlab platform.
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Bayesian identification of multiple seismic change points and varying seismic rates caused by induced Seismicity
Geophysical Research Letters, 2017Co-Authors: Silvana Montoya-noguera, Yu WangAbstract:The Central and Eastern United States (CEUS) has experienced an abnormal increase in seismic activity, which is believed to be related to anthropogenic activities. The U.S. Geological Survey has acknowledged this situation and developed the CEUS 2016 1 year seismic hazard model using the catalog of 2015 by assuming stationary Seismicity in that period. However, due to the nonstationary nature of induced Seismicity, it is essential to identify change points for accurate probabilistic seismic hazard analysis (PSHA). We present a Bayesian procedure to identify the most probable change points in Seismicity and define their respective seismic rates. It uses prior distributions in agreement with conventional PSHA and updates them with recent data to identify Seismicity changes. It can determine the change points in a regional scale and may incorporate different types of information in an objective manner. It is first successfully tested with simulated data, and then it is used to evaluate Oklahoma's regional Seismicity.
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Bayesian identification of multiple seismic change points and varying seismic rates caused by induced Seismicity
Geophysical Research Letters, 2017Co-Authors: Silvana Montoya-noguera, Yu WangAbstract:The Central and Eastern United States (CEUS) has experienced an abnormal increase in seismic activity, which is believed to be related to anthropogenic activities. The U.S. Geological Survey has acknowledged this situation and developed the CEUS 2016 1 year seismic hazard model using the catalog of 2015 by assuming stationary Seismicity in that period. However, due to the nonstationary nature of induced Seismicity, it is essential to identify change points for accurate probabilistic seismic hazard analysis (PSHA). We present a Bayesian procedure to identify the most probable change points in Seismicity and define their respective seismic rates. It uses prior distributions in agreement with conventional PSHA and updates them with recent data to identify Seismicity changes. It can determine the change points in a regional scale and may incorporate different types of information in an objective manner. It is first successfully tested with simulated data, and then it is used to evaluate Oklahoma's regional Seismicity.
A. Helmstetter - One of the best experts on this subject based on the ideXlab platform.
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Importance of direct and indirect triggered Seismicity in the ETAS model of Seismicity
Geophysical Research Letters, 2003Co-Authors: A. Helmstetter, D. SornetteAbstract:Using the simple ETAS branching model of Seismicity, which assumes that each earthquake can trigger other earthquakes, we quantify the role played by the cascade of triggered Seismicity in controlling the rate of aftershock decay as well as the overall level of Seismicity in the presence of a constant external Seismicity source.We show that, in this model, the fraction of earthquakes in the population that are aftershocks is equal to the fraction of aftershocks that are indirectly triggered and is given by the average number of triggered events per earthquake. Previous observations that a significant fraction of earthquakes are triggered earthquakes therefore imply that most aftershocks are indirectly triggered by the mainshock. INDEX TERMS: 7209 Seismology: Earthquake dynamics and mechanics; 7223 Seismology: Seismic hazard assessment and prediction; 7260 Seismology: Theory and modeling.
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Foreshocks Explained by Cascades of Triggered Seismicity
Journal of Geophysical Research, 2003Co-Authors: A. Helmstetter, D. SornetteAbstract:The observation of foreshocks preceding large earthquakes and the suggestion that foreshocks have specific properties that may be used to distinguish them from other earthquakes have raised the hope that large earthquakes may be predictable. Among proposed anomalous properties are the larger proportion than normal of large versus small foreshocks, the power law acceleration of Seismicity rate as a function of time to the mainshock and the spatial migration of foreshocks toward the mainshock, when averaging over many sequences. Using Southern California Seismicity, we show that these properties and others arise naturally from the simple model that any earthquake may trigger other earthquakes, without arbitrary distinction between foreshocks, aftershocks and mainshocks. We find that foreshocks precursory properties are independent of the mainshock size. This implies that earthquakes (large or small) are predictable to the same degree as Seismicity rate is predictable from past Seismicity by taking into account cascades of triggering. The cascades of triggering give rise naturally to long-range and long-time interactions, which can explain the observations of correlations in Seismicity over surprisingly large length scales.
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Predictability in the ETAS Model of Interacting Triggered Seismicity
Journal of Geophysical Research, 2003Co-Authors: A. Helmstetter, D. SornetteAbstract:As part of an effort to develop a systematic methodology for earthquake forecasting, we use a simple model of Seismicity based on interacting events which may trigger a cascade of earthquakes, known as the Epidemic-Type Aftershock Sequence model (ETAS). The ETAS model is constructed on a bare (unrenormalized) Omori law, the Gutenberg-Richter law and the idea that large events trigger more numerous aftershocks. For simplicity, we do not use the information on the spatial location of earthquakes and work only in the time domain. We demonstrate the essential role played by the cascade of triggered Seismicity in controlling the rate of aftershock decay as well as the overall level of Seismicity in the presence of a constant external Seismicity source. We offer an analytical approach to account for the yet unobserved triggered Seismicity adapted to the problem of forecasting future seismic rates at varying horizons from the present. Tests presented on synthetic catalogs validate strongly the importance of taking into account all the cascades of still unobserved triggered events in order to predict correctly the future level of Seismicity beyond a few minutes. We find a strong predictability if one accepts to predict only a small fraction of the large-magnitude targets. Specifically, we find a prediction gain (defined as the ratio of the fraction of predicted events over the fraction of time in alarms) equal to 21 for a fraction of alarm of 1%, a target magnitude M ≥ 6, an update time of 0.5 days between two predictions, and for realistic parameters of the ETAS model. However, the probability gains degrade fast when one attempts to predict a larger fraction of the targets. This is because a significant fraction of events remain uncorrelated from past Seismicity. This delineates the fundamental limits underlying forecasting skills, stemming from an intrinsic stochastic component in these interacting triggered Seismicity models. Quantitatively, the fundamental limits of predictability found here are only lower bounds of the true values corresponding to the full information on the spatial location of earthquakes.
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Is Earthquake Triggering Driven by Small Earthquakes?
Physical Review Letters, 2003Co-Authors: A. HelmstetterAbstract:Using a catalog of Seismicity for Southern California, we measure how the number of triggered earthquakes increases with the earthquake magnitude. The trade-off between this relation and the distribution of earthquake magnitudes controls the relative role of small compared to large earthquakes. We show that Seismicity triggering is driven by the smallest earthquakes, which trigger fewer events than larger earthquakes, but which are much more numerous. We propose that the non-trivial scaling of the number of triggered earthquakes emerges from the fractal spatial distribution of Seismicity.
D. Sornette - One of the best experts on this subject based on the ideXlab platform.
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Importance of direct and indirect triggered Seismicity in the ETAS model of Seismicity
Geophysical Research Letters, 2003Co-Authors: A. Helmstetter, D. SornetteAbstract:Using the simple ETAS branching model of Seismicity, which assumes that each earthquake can trigger other earthquakes, we quantify the role played by the cascade of triggered Seismicity in controlling the rate of aftershock decay as well as the overall level of Seismicity in the presence of a constant external Seismicity source.We show that, in this model, the fraction of earthquakes in the population that are aftershocks is equal to the fraction of aftershocks that are indirectly triggered and is given by the average number of triggered events per earthquake. Previous observations that a significant fraction of earthquakes are triggered earthquakes therefore imply that most aftershocks are indirectly triggered by the mainshock. INDEX TERMS: 7209 Seismology: Earthquake dynamics and mechanics; 7223 Seismology: Seismic hazard assessment and prediction; 7260 Seismology: Theory and modeling.
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Foreshocks Explained by Cascades of Triggered Seismicity
Journal of Geophysical Research, 2003Co-Authors: A. Helmstetter, D. SornetteAbstract:The observation of foreshocks preceding large earthquakes and the suggestion that foreshocks have specific properties that may be used to distinguish them from other earthquakes have raised the hope that large earthquakes may be predictable. Among proposed anomalous properties are the larger proportion than normal of large versus small foreshocks, the power law acceleration of Seismicity rate as a function of time to the mainshock and the spatial migration of foreshocks toward the mainshock, when averaging over many sequences. Using Southern California Seismicity, we show that these properties and others arise naturally from the simple model that any earthquake may trigger other earthquakes, without arbitrary distinction between foreshocks, aftershocks and mainshocks. We find that foreshocks precursory properties are independent of the mainshock size. This implies that earthquakes (large or small) are predictable to the same degree as Seismicity rate is predictable from past Seismicity by taking into account cascades of triggering. The cascades of triggering give rise naturally to long-range and long-time interactions, which can explain the observations of correlations in Seismicity over surprisingly large length scales.
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Predictability in the ETAS Model of Interacting Triggered Seismicity
Journal of Geophysical Research, 2003Co-Authors: A. Helmstetter, D. SornetteAbstract:As part of an effort to develop a systematic methodology for earthquake forecasting, we use a simple model of Seismicity based on interacting events which may trigger a cascade of earthquakes, known as the Epidemic-Type Aftershock Sequence model (ETAS). The ETAS model is constructed on a bare (unrenormalized) Omori law, the Gutenberg-Richter law and the idea that large events trigger more numerous aftershocks. For simplicity, we do not use the information on the spatial location of earthquakes and work only in the time domain. We demonstrate the essential role played by the cascade of triggered Seismicity in controlling the rate of aftershock decay as well as the overall level of Seismicity in the presence of a constant external Seismicity source. We offer an analytical approach to account for the yet unobserved triggered Seismicity adapted to the problem of forecasting future seismic rates at varying horizons from the present. Tests presented on synthetic catalogs validate strongly the importance of taking into account all the cascades of still unobserved triggered events in order to predict correctly the future level of Seismicity beyond a few minutes. We find a strong predictability if one accepts to predict only a small fraction of the large-magnitude targets. Specifically, we find a prediction gain (defined as the ratio of the fraction of predicted events over the fraction of time in alarms) equal to 21 for a fraction of alarm of 1%, a target magnitude M ≥ 6, an update time of 0.5 days between two predictions, and for realistic parameters of the ETAS model. However, the probability gains degrade fast when one attempts to predict a larger fraction of the targets. This is because a significant fraction of events remain uncorrelated from past Seismicity. This delineates the fundamental limits underlying forecasting skills, stemming from an intrinsic stochastic component in these interacting triggered Seismicity models. Quantitatively, the fundamental limits of predictability found here are only lower bounds of the true values corresponding to the full information on the spatial location of earthquakes.
Jean-robert Grasso - One of the best experts on this subject based on the ideXlab platform.
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How is Volcano Seismicity Different from Tectonic Seismicity?
Bulletin of the Seismological Society of America, 2010Co-Authors: Paola Traversa, Jean-robert GrassoAbstract:We analyze the temporal patterns of volcano Seismicity using the statistics of waiting times between subsequent earthquakes. We compare waiting time distributions of Seismicity at Mt. Etna and Mt. Vesuvius volcanoes during (1) inter-eruption phases and (2) dyke propagations, with those of tectonic Seismicity using the southern California catalog. For inter-eruption phases, no matter their duration, statistics of inter-event times are well approximated by the gamma distribution. This allows us to compute the proportion of background uncorrelated events (Molchan, 2005; Hainzl et al., 2006), which is recovered in the range 20%-40% for Vesuvius, three Etna inter-eruptive periods, and the southern California catalog. It argues for roughly 70% of earthquake activity to be cascades of aftershocks for both volcano inter-eruptive and tectonic Seismicity. On the contrary, statistics of inter-event times recorded during both the 2001 and 2002 intrusive episodes at the Etna volcano reject the gamma distribution to describe the observations. These seismic crises are characterized by an average Seismicity rate about 2 orders of magnitude larger than that of inter-eruptive periods. It suggests that the origin of the specificity of waiting time patterns during dyke injections is driven by the external forcing rate. Using the epydemic type aftershock sequences model simulations we explore the effect of Seismicity rate increases on inter-event time distributions. Departures from the gamma law progressively emerges from both (1) an increase of the background Seismicity rate and (2) a screening effect. It prevents us from quantifying the portion of uncorrelated Seismicity within the considered catalog and from clearly quantifying the forcing rate that characterizes the volcano dynamics during dyke intrusions.
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Brittle Creep Damage as the Seismic Signature of Dyke Propagations within Basaltic Volcanoes
Bulletin of the Seismological Society of America, 2009Co-Authors: Paola Traversa, Jean-robert GrassoAbstract:Contemporary to nine dyke intrusions on Piton de la Fournaise, Etna, and Miyakejima volcanoes, we recover stationary Seismicity rate and energy release over time, whether the dyke reaches the surface or not. This generic Seismicity pattern for the dyke propagation of low viscosity magma argues for the fluid driven crack propagation to be a scale independent stationary process. This prevents any prediction of the time to eruption during the dyke propagation phase using Seismicity rate alone. The seismic signature of the volcano deformation triggered by dyke injections corresponds to brittle creep damage in a strain driven setting. Whether mechanical properties of host rock structure or geometrical effects influence this generic stationary response is not resolved by the seismic data. Because a few, if any, aftershocks are resolved contemporary to dyke intrusion, the Seismicity is purely driven by the dyke dynamics, that is, a proxy for the dyke volumetric growth.
Frederic Gueydan - One of the best experts on this subject based on the ideXlab platform.
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Control of tectonic inheritance on continental intraplate strain rate and Seismicity
Tectonophysics, 2018Co-Authors: Stephane Mazzotti, Frederic GueydanAbstract:Present-day deformation and Seismicity of continental lithosphere are characterized by a first-order dichotomy between Plate Boundary Zones (PBZ) and Stable Continental Regions (SCR). Whereas the former are associated with high strain and Seismicity rates, the latter tend to remain un-deformed, except in localized regions of higher strain and Seismicity, commonly related to fossilized paleo-PBZ acting as locally weaker domains. Because of their low amplitudes, these intraplate strain and Seismicity rates are particularly difficult to measure and characterize. In this study, we propose a simple model to explain and quantify first-order continental strain rate variations, focusing on intraplate regions. Assuming near-failure equilibrium on 1D lithosphere profiles, we derive steady-state strain rates driven by tectonic forces as a function of rheological models that include new strain-weakening rheologies in order to simulate tectonic inheritance. Within this framework, inherited strain-weakening plays a fundamental role in allowing for and explaining strain and Seismicity concentration in intraplate weak zones: our model predicts strain rates in intraplate weak zones up to two to three orders of magnitude higher compared to stable cratons due to the effect of tectonic inheritance on rheology weakening. These model predictions are in agreement with empirical estimations in intraplate regions and can provide a conceptual framework for characterization of SCR strain and Seismicity rates.
